9.9.3.    Designated Sites

56. Where Natura 2000 sites (i.e. nature conservation sites in Europe designated under the Habitats or Birds Directives[4]; or sites in the UK that comprise the National Site Network (collectively termed ‘European sites’) are considered, this chapter makes an assessment of the likely significant effects in EIA terms on the qualifying interest feature(s) of these sites as described within section 9.7.2 of this chapter. The assessment of the of the potential impacts on the site itself are deferred to the RIAA (SSER, 2022c) for the Proposed Development. A summary of the outcomes reported in the RIAA is provided in section 9.15 of this chapter.
57. With respect to locally designated sites and national designations (other than European sites), where these sites fall within the boundaries of a European site and where qualifying interest features are the same, only the features of the European site have been taken forward for assessment. This is because potential impacts on the integrity and conservation status of the locally or nationally designated site are assumed to be inherent within the assessment of the features of the European site (i.e. a separate assessment for the local or national site features is not undertaken). However, where a local or nationally designated site falls outside the boundaries of a European site, but within the Proposed Development northern North Sea fish and shellfish ecology study area, an assessment of the likely significant effects on the overall site is made in this chapter using the EIA methodology.

9.10. Measures Adopted as part of the Proposed Development

58. As part of the project design process, a number of measures have been proposed to reduce the potential for impacts on fish and shellfish ecology (see Table 9.20   Open ▸ ). As there is a commitment to implementing these measures, they are considered inherently part of the design of the Proposed Development and have therefore been considered in the assessment presented in section 9.11 (i.e. the determination of magnitude and therefore significance assumes implementation of these measures). These measures are considered standard industry practice for this type of development.

Table 9.20: Designed In Measures Adopted as Part of the Proposed Development

9.11. Assessment of Significance

59. The potential effects arising from the construction, operation and maintenance and decommissioning phases of the Proposed Development are listed in Table 9.15   Open ▸ , along with the maximum design scenario against which each impact has been assessed. An assessment of the likely significance of the effects of the Proposed Development on fish and shellfish ecology IEFs caused by each identified impact is given below.

Temporary Subtidal Habitat loss/disturbance

60. Direct temporary habitat loss/disturbance of subtidal seabed habitats within the Proposed Development array area and offshore export cable corridor during the construction, operation and maintenance, and decommissioning phases will occur as a result of a range of activities including use of jack-up vessels during foundation installation/maintenance, installation and maintenance of inter-array and offshore export cables (including seabed clearance operations prior to cable installation) and anchor placements associated with these activities. Disturbance to these habitats has the potential to affect identified fish and shellfish IEFs directly (e.g. removal or injury of individuals) and indirectly (e.g. loss of important fish and shellfish habitats, such as spawning grounds).
61. Seabed preparation activities, including sand wave clearance and boulder clearance, will occur in advance of installation of inter-array cables and offshore export cables. Dredged material resulting from seabed preparations will be disposed of within the Proposed Development. The assessment therefore includes habitat loss/disturbance associated with disposal of dredged material from this activity, (i.e. habitat loss/disturbance due to placement of large volumes of coarse sediments on the seabed (see Table 9.15   Open ▸ )). Effects on areas of seabed which have been subject to seabed preparation activities prior to foundation installation have been assessed under long term subtidal habitat loss as the area of seabed affected by seabed preparation will be the same area on which foundations (and potentially scour protection) will be placed for the lifetime of the Proposed Development.

Construction Phase

Magnitude of Impact

62. The installation of infrastructure within the Proposed Development fish and shellfish ecology study area may lead to temporary subtidal habitat loss/disturbance. The maximum design scenario is for up to 113,974,700 m2 of temporary habitat loss/disturbance during the construction phase ( Table 9.15   Open ▸ ). This equates to 9.7% of the Proposed Development, representing a relatively small proportion of the Proposed Development fish and shellfish ecology study area. It should be noted that only a small proportion of the total footprint will be affected at any one time during the 96 months construction phase, with recovery of seabed habitats commencing immediately following installation of infrastructure.
63. Temporary habitat loss of up to 42,948,000 m2 will also occur as a result of the installation of up to 1,225 km of inter-array cables, 94 km of OSP/Offshore convertor substation platform interconnector cables and up to 872 km of offshore export cables. Sand wave clearance may be required for up to 20% of the Proposed Development export cable corridor length and up to 30% of inter-array cables and OSP/Offshore convertor substation platform interconnector cables. Boulder clearance may be required for up to 20% of offshore export cables length, inter-array cables and OSP/Offshore convertor substation platform interconnector cable ( Table 9.15   Open ▸ ). The maximum width of seabed preparation is greater than the disturbance associated with the cable installation itself to allow enough space to operate the tool (i.e. 15 m for cable burial, 25 m for boulder clearance and 25 m for sand wave clearance). Cable burial will therefore occur within the area previously disturbed via sand wave or boulder clearance resulting in localised repeat disturbance within a 15 m wide corridor, within the wider 25 m corridor disturbed during sand wave and boulder clearance.
64. A recent review commissioned by The Crown Estate (TCE) reviewed the effects of cable installation on subtidal sediments and habitats (RPS, 2019), drawing on monitoring reports from over 20 UK offshore wind farms. This review showed that sandy sediments recover quickly following cable installation, with trenches infilling quickly following cable installation and little or no evidence of disturbance in the years following cable installation. It also presented evidence that in some settings, remnant cable trenches in coarse and mixed sediments and muddy sediments were conspicuous for several years after installation. However, these shallow depressions were of limited depth (i.e. tens of cm) relative to the surrounding seabed, over a horizontal distance of several metres and therefore did not represent a large shift from the baseline environment (RPS, 2019).
65. As set out in Table 9.15   Open ▸ , the maximum design scenario assumes the removal of up to 14 UXO from the Proposed Development. These clearance activities would however occur within the footprint of other seabed clearance works (i.e. sand wave and boulder clearance), cable burial activities and/or foundation footprints and therefore will not lead to additional habitat disturbance. Any craters created during detonation are expected to backfill by natural processes, the speed of which would depend on the sediment transport regimes in the area.
66. Anchor footprints from cable installation vessels will also result in habitat disturbance. Typically, one anchor reposition per 500 m of cable may be required, with individual anchors associated with cable installation vessels having a footprint of approximately 100 m2. This area of seabed disturbance will depend on the precise vessel used and in some cases anchor placements may not be required at all (e.g. where the vessel uses dynamic positioning). The maximum design scenario accounts for up to 438,200 m2 of temporary disturbance from a 100 m2 anchor placed every 500 m during inter-array, OSP/Offshore convertor substation platform interconnector and offshore export cables installation.
67. Jack-up footprints associated with foundation installation will result in compression of seabed sediments beneath spud cans where these are placed on the seabed. These will infill over time, although may remain on the seabed for a number of years, as demonstrated by monitoring studies of UK offshore wind farms (BOWind, 2008; EGS, 2011). Monitoring at the Barrow offshore wind farm showed depressions were almost entirely infilled 12 months after construction (BOWind, 2008). Monitoring at Lynn and Inner Dowsing offshore wind farm also showed some infilling of the footprints, although the depressions (i.e. of the order of tens of centimetres) were still visible a couple of years post construction (EGS, 2011). In areas where mobile sands and coarse sediments are present such as in the majority of the Proposed Development fish and shellfish ecology study area (see volume 2, chapter 8), jack-up depressions are likely to be temporary features which will only persist for a period of months to a small number of years.
68. Activities resulting in the temporary subtidal habitat loss/disturbance will occur intermittently throughout the construction phase. The offshore construction phase which includes activities resulting in temporary habitat loss/disturbance will occur over a period of up to 96 months. Once construction in a local area (for example, a section of offshore export cable) has been completed, this area will not be disturbed further during the construction phase. This area will start to recover immediately following cessation of construction activities in the vicinity allowing mobile species, such as sandeel and other fish and shellfish species, to repopulate the areas of previous disturbance (see paragraph 78 et seq. for further discussion of recovery of species).
69. The impact is predicted to be of local spatial extent (i.e. limited to the Proposed Development fish and shellfish ecology study area), medium term duration (although only a small proportion of the total area will be affected at any one time with individual elements of construction having much shorter durations), intermittent and high reversibility. It is predicted that the impact will affect the receptor directly or indirectly, dependent on species’ life strategies. The magnitude is therefore considered to be low.

Sensitivity of the Receptor

Marine species

70. In general, mobile fish species are able to avoid areas subject to temporary habitat disturbance (EMU, 2004). The most vulnerable species are likely to be shellfish which are much less mobile than fish. For example, egg bearing lobster are thought to be more restricted to an area based on a mark and recapture study in Norway which showed that 84% of berried female lobster remained within 500 m of their release site (Agnalt et al., 2007). Evidence from other stocks around the world are less clear, with limited movement recorded for some stocks and long distance migrations documented for other stocks (e.g. Campbell and Stasko,1985; Comeau and Savoie, 2002).
71. Indirect effects on fish and shellfish species also include loss of feeding habitat and prey items. For example, crabs and other crustaceans and small benthic fish species (as well as other benthic species; see volume 2, chapter 8) are considered important prey species for larger fish. However, since this impact is predicted to affect only a small proportion of seabed habitats in the Proposed Development fish and shellfish ecology study area at any one time, with similar habitats (and prey species) occurring throughout the Forth and Tay SMR and the wider Proposed Development northern North Sea fish and shellfish ecology study area, these effects are likely to be limited and highly reversible. Conversely, habitat disturbance during the construction phase will also expose benthic infaunal species from the sediment (see volume 2, chapter 8), potentially offering foraging opportunities to some fish and shellfish species (e.g. opportunistic scavenging species) immediately after completion of works. The implications of changes in fish and shellfish prey species are also discussed for higher trophic level receptors (i.e. marine mammals and birds) in volume 2, chapter 10 and chapter 11.
72. A number of commercially important shellfish species such as edible crab, lobster, Nephrops, scallop and velvet swimming crab are known to inhabit the Proposed Development fish and shellfish ecology study area. Habitat loss in this area will represent a relatively small temporary disturbance to these habitats (e.g. during cable laying and seabed preparation), with relatively rapid recovery of sediments (RPS, 2019), and following this, recovery of associated communities (see volume 2, chapter 8) including shellfish populations into these areas. The recoverability and rate of recovery of an area after large scale seabed disturbance (e.g. dredging or trawling activities) is linked to the substrate type (Newell et al., 1998; Desprez, 2000). Mud or sand habitats, similar to those found in the Proposed Development fish and shellfish ecology study area, have been shown to return to baseline species abundance after approximately one to two years (Newell et al., 1998; Desprez, 2000). Harder gravely and rocky substrate takes proportionally longer to re‑establish: up to ten years for boulder coastlines (Newell et al., 1998).
73. Larger crustacea (e.g. Nephrops, European lobster) are classed as equilibrium species (Newell et al., 1998) and are only capable of recolonising an area once the original substrate type has returned. The sensitivity of these fish and shellfish IEFs is therefore higher than for smaller benthic organisms which move in and colonise new substrate immediately after the effect. Therefore, although recovery of benthic assemblages may occur over relatively fast timescales (e.g. within one to two years; see volume 2, chapter 8), recovery of the equilibrium species may take up to ten years in some areas of coarse sediments (Phua et al., 2002).
74. Construction operations (including cable installation) within the Proposed Development fish and shellfish ecology study area may also impact on spawning and nursery habitats for Nephrops, as these areas overlap and have been mapped (i.e. broadscale mapping by Coull et al., 1998) as coinciding with the Proposed Development fish and shellfish ecology study area (volume 3, appendix 9.1). However, site-specific surveys showed that Nephrops were only recorded along the Proposed Development export cable corridor and therefore would only be affected by a relatively small proportion of the proposed construction operations. Further, larval settlement will also increase the rate of recovery in an area (Phua et al., 2002), with shellfish (Nephrops) spawning and nursery habitats in the vicinity of the Proposed Development fish and shellfish ecology study area (see volume 3, appendix 9.1) potentially increasing the rate of recovery into disturbed areas. A recent study undertaken during construction of the Westermost Rough Offshore Wind Farm located on the north-east coast of England, within a European lobster fishing ground, found that the size and abundance of lobster individuals increased following temporary closure or the area for construction of the wind farm. This study shows that the activities associated with construction of the wind farm, which included installation of wind turbines and cables, did not impact on resident lobster populations and instead allowed some respite from fishing activities for a short time period before reopening following construction (Roach et al., 2018).
75. Scallop are likely to be present within the Proposed Development fish and shellfish ecology study area and are targeted by commercial fisheries activities (see volume 2, chapter 12). Scallop are predominantly sessile organisms, however, they do have the ability to swim, which is ordinarily used as an escape response, although limited in distance (Marshall and Wilson, 2008). It has been documented the scallop have been able to move up to 30 m from a release site during a tagging study (Howell & Fraser, 1984). This response may allow improved resilience to temporary habitat loss/disturbance than other sessile organisms, by being able to avoid areas of disturbance and relocate to areas nearby. Scallop tend to occur in aggregations as their larval distribution is reliant on hydrographic features (Brand, 1991), therefore assuming scallop populations continue to spawn outside the boundary of the Proposed Development fish and shellfish ecology study area and within unimpacted areas of the Proposed Development, and suitable habitat for settlement remains, it is likely that scallop will continue to be recruited into the Proposed Development fish and shellfish ecology study area. Therefore, scallop will recover well from any disturbance due to short term habitat loss. This is supported by the MarLIN sensitivity assessment (Marshall and Wilson, 2008) which concluded scallops have a high recovery potential (i.e. recovery within months, with full recovery in a small number of years).
76. The fish species within the Proposed Development fish and shellfish ecology study area which are likely to be most sensitive to temporary habitat loss are those species which spawn on or near the seabed sediment (e.g. herring, sandeel and elasmobranchs, including spotted ray). Of the IEF fish species that spawn on or near the seabed, sandeel and herring are known to spawn at varying intensities within the vicinity of the Proposed Development fish and shellfish ecology study area (see volume 3, appendix 9.1). Therefore, seabed disturbance activities carried out during spawning periods may result in some mortality of eggs and reduced opportunity due to removal of suitable habitat. However, the area which will be disturbed is small given the abundance of similar substrate types and the extensive nature of fish spawning grounds across the Proposed Development northern North Sea fish and shellfish ecology study area.
77. Physical disturbance to sandeel habitats may also lead to direct effects on adult and juvenile sandeel (e.g. increased mortality), where individuals are not able to colonise viable sandy habitats in the immediate vicinity, or where habitats may be at carrying capacity (Wright et al., 2000). This is as identified by the FeAST tool as a pressure on sandeel ‘sub-surface abrasion/penetration’ which has noted that sandeel have high sensitivity to this impact (Wright et al., 2000). Sandeel may also be particularly vulnerable during their winter hibernation period when they bury themselves in the seabed substrates and are therefore less mobile. A large proportion of temporary habitat disturbance (60,342,400 m2) is related to construction activities within the Proposed Development export cable corridor. The majority of favourable and preferred sandeel habitat within the Proposed Development fish and shellfish ecology study area is located within the Proposed Development array area (as described in section 9.7). Therefore, a significant proportion of temporary habitat disturbance will take place within areas of less favourable habitat within the Proposed Development export cable corridor. The temporary subtidal habitat loss/disturbance in the Proposed Development array area alone equates to up to 53,632,300 m2. As a proportion of the Proposed Development array area, this accounts for up to 5.3%, which is a relatively small proportion in the context of available habitat in the Proposed Development array area and across the wider Firth and Tay SMR. Further, as noted above, only a small proportion of this maximum footprint of habitat loss/disturbance will be occurring at any one time during the construction phase, with recovery of sediments, and sandeel populations into them.
78. Recovery of sandeel populations would be expected following construction operations, with the rate of recovery dependent on the recovery of sediments to a condition suitable for sandeel recolonisation. Effects of offshore wind farm construction (Jensen et al., 2004) and operation (i.e. post-construction) (van Deurs et al., 2012) on sandeel populations have been examined through short term and long term monitoring studies at the Horns Rev offshore wind farm in the Baltic Sea, Denmark. These monitoring studies have shown that offshore wind farm construction and operation has not led to significant adverse effects on sandeel populations and that recovery of sandeel occurs quickly following construction operations.
79. The recovery potential of sandeel populations can also be inferred from a study by Jensen et al. (2010), which found sandeel populations mix within fishing grounds to distances of up to 28 km. This suggests that some recovery of adult populations is likely following construction operations, with adults recolonising suitable sandy substrates from adjacent un-impacted habitats. Recovery may also occur through larval recolonisation of suitable sandy sediments with sandeel larvae likely to be distributed throughout the Proposed Development fish and shellfish ecology study area during spring months following spawning in winter/spring (see Ellis et al., 2012; and volume 3, appendix 9.1).
80. A recent monitoring study conducted at the Beatrice Offshore Wind Farm completed a post construction sandeel survey where sandeel abundance were compared pre and post construction (BOWL, 2021a). The results showed that sandeel abundance either increased or remained at similar levels when comparing abundance from 2014 to 2020, with offshore construction commencing in April 2017. The study concluded that there was no evidence that the construction of Beatrice Offshore Wind Farm resulted in adverse impacts on the local sandeel population. This conclusion should be seen in the context of general increase in sandeel populations in the area surrounding the Beatrice Offshore Wind Farm (using ICES set Total Allowable Catch (TAC) as an indicator), and an increase in bycatch abundance from the sandeel dredging, which may indicate the Beatrice Offshore Wind Farm site was generally healthier in 2020 than it was in 2014 (BOWL, 2021a). This study builds on previous work conducted by Stenberg et al. (2011) which concluded that the construction of the Horns Rev 1 Offshore Wind Farm posed neither a threat nor direct benefit to sandeel over a seven-year period.
81. As described in paragraph 68, temporary habitat loss during the construction phase (96 months), will not occur simultaneously across the entire Proposed Development array area, rather only a small proportion of the maximum habitat loss/disturbance footprint will occur at a particular location at any one time. Once construction/infrastructure installation works are complete in a specific area, recovery of sediments and associated communities will begin. Drawing on information from the monitoring studies above, it is highly likely that the displaced individuals will repopulate these previously disturbed areas, with recovery occurring throughout the construction phase rather than once the entire construction phase is completed.
82. As effects on sandeel (and other prey species) are predicted to be limited in extent (particularly in the context of available habitats in the Proposed Development northern North Sea fish and shellfish ecology study area), temporary and reversible, with recovery of sandeel populations occurring post construction, species reliant on sandeel and other small prey species (e.g. sea trout and cod) would similarly not be expected to be significantly affected. The implications of changes in fish and shellfish prey species are also discussed for higher trophic level receptors (i.e. marine mammals and birds) in volume 2, chapter 10 and volume 2, chapter 11.
83. Herring spawning has been demonstrated to take place within the Proposed Development fish and shellfish ecology study area at a low intensity, with higher intensity spawning grounds being present to the north of the Proposed Development fish and shellfish ecology study area (see volume 3, appendix 9.1). Favourable habitat (gravel and sandy gravel) for spawning is present in patches within the Proposed Development fish and shellfish ecology study area, however, the area affected by temporary habitat loss (i.e. within the Proposed Development array area only) is dominated by sediments which are not suitable for herring spawning and therefore the area of herring spawning grounds affected by this impact is expected to be very limited, in the context of available favourable sediments habitat outside the Proposed Development fish and shellfish ecology study area and across the wider Proposed Development northern North Sea fish and shellfish ecology study area.
84. Most fish and shellfish ecology IEFs in the Proposed Development fish and shellfish ecology study area are deemed to be of low vulnerability, high recoverability and local to national importance. The sensitivity of the receptor is therefore, considered to be low.
85. European lobster and Nephrops are deemed to be of high vulnerability, medium to high recoverability and of regional importance. The sensitivity of these fish and shellfish IEFs is therefore considered to be medium.
86. Herring are deemed to be of high vulnerability, medium recoverability and of regional importance. However, the sensitivity of herring to this impact is considered to be low, due to the limited suitable spawning sediments overlapping with the Proposed Development fish and shellfish ecology study area and the core herring spawning ground being located well outside the Proposed Development fish and shellfish ecology study area.
87. Sandeel are deemed to be of high vulnerability, high recoverability and of national importance. The sensitivity of sandeel is therefore considered to be medium.

Diadromous Species

88. Diadromous fish species are highly mobile and therefore are generally able to avoid areas subject to temporary habitat loss. Diadromous species that are likely to interact with the Proposed Development fish and shellfish ecology study area are only likely to do so by passing through the area during migrations to and from rivers located on the east coast of Scotland, such as to rivers with designated sites, with diadromous fish species listed as qualifying features (see Table 9.12   Open ▸ and volume 3, appendix 9.1). The habitats within the Proposed Development fish and shellfish ecology study area are not expected to be particularly important for diadromous fish species and therefore habitat loss during the construction phase of the Proposed Development fish and shellfish ecology study area is unlikely to cause any direct impact to diadromous fish species and would not affect migration to and from rivers.
89. Indirect impacts on diadromous fish species may occur due to impacts on prey species, for example larger fish species for sea lamprey and sandeel for sea trout. As outlined for marine species above, the majority of large fish species would be able to avoid habitat loss effects due to their greater mobility but would recover into the areas affected following cessation of construction. Sandeel (and other less mobile prey species) would be affected by temporary habitat loss, although recovery of this species is expected to occur quickly as the sediments recover following installation of infrastructure and adults recolonise and also via larval recolonisation of the sandy sediments, which dominate the Proposed Development fish and shellfish ecology study area and are known to recover quickly following cable installation (RPS, 2019). Diadromous fish species are deemed to be of low vulnerability, high recoverability and national to international importance. The sensitivity of the receptor is therefore, considered to be low.

Significance of the Effect

Marine Species

90. Overall, the magnitude of the impact is deemed to be low and the sensitivity of most fish IEFs (including herring) is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
91. For sandeel, the magnitude of the impact is deemed to be low and the sensitivity is considered to be medium. The effect will, therefore, be of minor adverse significance which is not significant in EIA terms. Although, the total figure for the area of subtidal habitat loss/disturbance is high, it should be viewed with the following context:

• a large proportion of habitat loss occurs within the Proposed Development export cable corridor, where habitat is less favourable/unsuitable for sandeel; and
• the total habitat loss/disturbance will not occur simultaneously, rather it would be spread across the site over the entire 96 months construction phase, allowing recovery into disturbed areas to begin as soon as construction activity has ceased.
  92. For Nephrops and European lobster, the magnitude of the impact is deemed to be low and the sensitivity is considered to be medium. The effect will, therefore, be of minor adverse significance which is not significant in EIA terms. It should be noted that there is some conservatism in this conclusion, specifically:
• Nephrops are distributed across only part of the Proposed Development export cable corridor, with more extensive habitats outside the Proposed Development fish and shellfish ecology study area and therefore would not be affected by the majority of the construction operations, particularly those occurring within the Proposed Development array area which are not suitable habitats for Nephrops; and
• similarly, lobster are likely to be targeted in nearshore areas including sections of the offshore export cable route. There is some creeling activity (which targets lobster and crab species) (see volume 3, appendix 12.1) within the Proposed Development array area, however lobster are typically associated with coarser sediments than those found within the Proposed Development fish and shellfish ecology study area and, it is likely that the creeling effort is focused on crab species rather than lobster.

Diadromous Species

93. Overall, the magnitude of the impact is deemed to be low and the sensitivity of the receptor is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

94. No additional fish and shellfish ecology mitigation is considered necessary as recovery of sediments and associated fish and shellfish IEFs will occur naturally without any need for further interventions and the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.

Operation and Maintenance Phase

Magnitude of Impact

95. Operation and maintenance activities within Proposed Development fish and shellfish ecology study area may lead to temporary subtidal habitat loss/disturbance. The maximum design scenario is for up to 989,000 m2 of temporary habitat loss/disturbance during the operation and maintenance phase ( Table 9.15   Open ▸ ). This equates to 0.08% of the Proposed Development and therefore this represents a very small proportion of the Proposed Development fish and shellfish ecology study area. It should also be noted that only a small proportion of the total habitat loss/disturbance is likely to be occurring at any one time over the 35-year operation phase of the Proposed Development.
96. Temporary habitat loss will occur as a result of the use of jack-up vessels during any component replacement activities and during any inter-array, OSP/Offshore convertor substation platform interconnector and offshore export cable repair activities. Impacts of jack-up vessel activities will be similar to those identified for the construction phase above and will be restricted to the immediate area around the wind turbine foundation or cable repair site, where the spud cans are placed on the seabed, with recovery occurring following removal of spud cans. Inter-array and offshore export cable repair or reburial activities will also affect habitats in the immediate vicinity of these operations, with effects on seabed habitats also expected to be similar to the construction phase. The spatial extent of this impact is very small in relation to the Proposed Development fish and shellfish ecology study area, although there is the potential for repeat disturbance to the habitats because of these activities (e.g. placement of spud cans on or in close proximity to where these were placed during construction; remedial burial of a length of cable installed during the construction phase, affecting the same area of seabed). Activities resulting in the temporary subtidal habitat loss/disturbance will occur intermittently throughout the 35-year operation and maintenance phase.
97. The impact is predicted to be of local spatial extent, short term duration (individual maintenance operations would occur over the period of days to weeks), intermittent and high reversibility. It is predicted that the impact will affect the receptor directly or indirectly, dependent on species’ life strategies. The magnitude is therefore considered to be negligible.

Sensitivity of the Receptor

98. The sensitivity of the fish and shellfish IEFs, for both marine and diadromous species, can be found in the construction phase assessment (see paragraph 70 et seq.), ranging from negligible to medium sensitivity.

Significance of the Effect

Marine Species

99. Overall, the magnitude of the impact is deemed to be negligible and the sensitivity of most fish IEFs (including herring) is considered to be low. The effect will, therefore, be of negligible to minor adverse significance, which is not significant in EIA terms.
100. For sandeel, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be medium. The effect will, therefore, be of negligible to minor adverse significance, which is not significant in EIA terms.
101. For Lobster and Nephrops, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be medium. The effect will, therefore, be of negligible to minor adverse significance, which is not significant in EIA terms.

Diadromous Species

102. Overall, the magnitude of the impact is deemed to be negligible and the sensitivity of the receptor is considered to be low. The effect will, therefore, be of negligible adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

103. No additional fish and shellfish ecology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.

Decommissioning Phase

Magnitude of Impact

104. Decommissioning activities within the Proposed Development fish and shellfish ecology study area may lead to temporary subtidal habitat loss/disturbance. The decommissioning activities includes jack-up vessels during foundation removal, removal of inter-array, interconnector and offshore export cables, and associated anchor placements during said cables removal. The maximum design scenario is for up to 34,571,200 m2 of temporary habitat loss/disturbance is during the decommissioning phase ( Table 9.15   Open ▸ ). This equates to 2.9% of the Proposed Development, with only a small proportion of this total area affected at any one time during the decommissioning phase. For the purposes of this assessment, the impacts of decommissioning are predicted to be similar to those for the construction phase (see paragraph 62 et seq.), although expected to be considerably less as seabed clearance may not be required.
105. The impact is predicted to be of local spatial extent (within the boundaries of the Proposed Development fish and shellfish ecology study area), medium term duration (although only a small proportion of the total area will be affected at any one time with individual elements of decommissioning having much shorter durations), intermittent and high reversibility. It is predicted that the impact will affect the receptor directly or indirectly, dependent on species’ life strategies. The magnitude is therefore considered to be low.

Sensitivity of the Receptor

106. The sensitivity of the fish and shellfish IEFs, for both marine and diadromous species, can be found in the construction phase assessment (see paragraph 70 et seq.) ranging from negligible to medium sensitivity.

Significance of the Effect

Marine Species

107. Overall, the magnitude of the impact is deemed to be low and the sensitivity of most fish IEFs (including herring) is considered to be low. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
108. For sandeel, the magnitude of the impact is deemed to be low and the sensitivity is considered to be medium. The effect will, therefore, be of minor adverse significance which is not significant in EIA terms.
109. For Nephrops and European lobster, the magnitude of the impact is deemed to be low and the sensitivity is considered to be medium. The effect will, therefore, be of minor adverse significance which is not significant in EIA terms. It should be noted that there is some conservatism in this conclusion, specifically:

Diadromous Species

110. Overall, the magnitude of the impact is deemed to be low and the sensitivity of the receptors is considered to be low. The effect will, therefore, be of negligible to minor adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

111. No additional fish and shellfish ecology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.

Increased suspended sediment concentrations and associated sediment deposition

112. Increases in SSC and associated sediment deposition are predicted to occur during the construction and decommissioning phases as a result of seabed preparation, the installation/removal of foundations and installation/removal of inter-array, interconnector and offshore export cables. Increases in suspended sediments and associated sediment deposition are also predicted to occur during the operation and maintenance phase due to inter-array and offshore export cable repair and reburial events. Volume 3, appendix 7.1 provides a full description of the physical processes baseline characterisation, including numerical modelling used to inform the predictions made with respect to increases in suspended sediment and subsequent deposition.

Construction Phase

Magnitude of Impact

113. The installation of infrastructure within the Proposed Development fish and shellfish ecology study area may lead to increases SSC and associated sediment deposition. Full details of the modelling undertaken to inform this assessment is presented in volume 3, appendix 7.1, including the individual scenarios considered and assumptions within these and full modelling outputs for suspended sediments and associated sediment deposition. For the purposes of this assessment, the following activities have been considered:

• seabed feature clearance prior to cable installation;
• drilling for foundation installation; and
• inter-array, OSP/Offshore convertor substation platform interconnector, and offshore export cable installation.
  114. Sand wave clearance for cable installation would involve disturbance of seabed material within a corridor of up to 25 m width for the 20% the Proposed Development offshore export cables, where it is necessary. Modelling of suspended sediments to quantify the potential increases in SSC and sedimentation during sand wave clearance simulated the use of a suction hopper dredger to remove material from the crest of sand waves and deposit material in the adjacent trough. Modelling associated with the site preparation showed a large variation. SSC reaches its peak in the disposal phase with concentrations reaching 2,500 mg/l at the release site, but the plume is at its most extensive when the deposited material is redistributed on the successive tides, under these circumstance concentrations of 100 mg/l to 250 mg/l have been modelled (see volume 3 appendix 7.1 for further details on modelling assumptions for SSC). The average SSC during the course of the clearance activities is presented in volume 3, appendix 7.1, with values less than 100 mg/l with a plume width of 10 km. Sedimentation of deposited material is focussed within 100 m of the site of release with a maximum depth 0.5 m – 0.75 m (this is considered within temporary habitat loss, see paragraph 62 et seq. and Table 9.15   Open ▸ ) whilst the finer sediment fractions are distributed in the vicinity at much lesser depths circa 5 mm – 10 mm within a range of hundreds of meters to a small number of kilometres. Sedimentation one day following cessation of operation is similar to during operation with a small extension to the area over which sedimentation has occurred but with no increase in maximum sedimentation depth (physical processes modelling detailed in volume 3, appendix 7.1). The dispersion of the released material would continue on successive tides and be incorporated into the baseline sediment transport regime, returning to background levels within a few tides.
  115. The maximum design scenario for the inter-array cable sand wave clearance also accounts for up to a 25 m wide corridor. The resulting SSC showed similar characteristics to the offshore export cables clearance. At the Proposed Development array area, the greatest area of increased SSC was also shown to be associated with re-mobilisation of the deposited material on subsequent tides. In this scenario, the plume was found to extend 10 km from the site, with peak concentrations of 100 mg/l – 250 mg/l and average levels are less than 100 mg/l. Again, SSCs were predicted to reach their peak in the dumping phase with concentrations reaching 2,500 mg/l at the release site. The average sedimentation depth is typically half that of the offshore export cable works, with maximum sedimentation of 100 –m - 300 mm, which is only reached in very small areas along the Proposed Development export cable corridor, and almost all within the Proposed Development fish and shellfish ecology study area. The sedimentation one day following the cessation of the clearance operation shows deposited material at the site of release with depth 0.2 m – 0.4 m (this is considered within temporary habitat loss, see paragraph 62 et seq. and Table 9.15   Open ▸ ) whilst in the locality, lower depths, typically less than 5 mm, are present at 50 m distance from the release. The dispersion of the released material would continue on successive tides and be incorporated into the baseline sediment transport regime, returning to background levels within a few tides.
  116. The maximum design scenario for foundation installation assumes all wind turbine and OSP/Offshore convertor substation platform foundations will be installed by drilling 5.5 m diameter piles for jacket foundations ( Table 9.15   Open ▸ ). Drilling was modelled for three wind turbines at different locations in the Proposed Development array area. The locations represent the dominant physical environmental conditions experienced in the Proposed Development array area. Modelling of SSCs associated with the foundation installation showed the plume related directly to the sediment releases was less than 5 mg/l and this drops to lower levels within a very short distance, typically less than 500 m. Furthermore, these sediment plumes are predicted to be temporary, returning to background levels within a few tides. The maximum sedimentation depth is typically 0.05 mm to 0.1 mm during pile installation, with that maximum dropping to 0.0005 mm – 0.001 mm one day following cessation of operations. These demonstrate the dispersive nature of the site, dispersing material the full extent of the tidal excursion (12 km), and even using a very small contour interval this settlement would be imperceptible from the background sediment transport activity with plotted sediment depths less than typical grain diameters.
  117. The maximum design scenario for the installation of inter-array and OSP/Offshore convertor substation platform interconnector cables assumes installation of all cables through jet trenching, with assumptions (e.g. trench width and depth) summarised in Table 9.15   Open ▸ . Modelling was undertaken for installation of inter-array and OSP/Offshore convertor substation platform interconnector cables along a number of paths which connect groups of wind turbines to OSP/Offshore convertor substation platforms or connect two OSP/Offshore convertor substation platforms to each other. Each route would be undertaken as a separate operation and thus a single example has been selected to quantify the potential suspended sediment levels during the installation. The inter-array cabling was modelled along a route with a trench 2 m wide and 3 m in depth. The modelling outputs for SSCs associated with the installation of cabling showed a very wavy plume extending from trenching route, the majority of which sits within the Proposed Development array area. It is clear that the sediment is re-suspended and dispersed on subsequent tides as the plume envelope is most extensive towards the start of the route to the south-east of the site with peak values of 100 mg/l extending hundreds of meters to a small number of kilometres. The volume of material mobilised is relatively large, and elevated tidal currents disperse the material giving rise to concentrations of up to 500 mg/l. The sedimentation is greatest at the location of the trenching and may be up to 30 mm in depth however within close proximity, circa 100 m, the depths reduce significantly.
  118. The modelling for offshore export cables also took a precautionary approach, assuming that cable installation would involve disturbance of seabed material up to 2 m wide and up to 3 m deep. Modelling outputs indicated average SSC along the route ranged between 50 mg/l and 500 mg/l. Average sedimentation peaks at 0.5 mm - 1.0 mm during offshore export cable installation and one day after cessation of operations this maximum increased to 10 mm - 30 mm, however this only accounts for a very small area with most of the impacted area displaying deposition depths considerably reduced at distance from the cable trench, returning to background levels within a few tides.
  119. The impact is predicted to be of local spatial extent (i.e. largely within the Proposed Development fish and shellfish ecology study area boundaries), short term duration, intermittent during the construction phase and high reversibility. It is predicted that the impact will affect the receptors directly. The magnitude is therefore considered to be low.

Sensitivity of the Receptor

Marine Species

120. In terms of SSC, adult fish species are more mobile than many of the other fish and shellfish IEFs, and therefore may show avoidance behaviour within areas affected by increased SSC (EMU, 2004), making them less susceptible to physiological effects of this impact. Juvenile fish are more likely to be affected by habitat disturbances such as increased SSC than adult fish. This is due to the decreased mobility of juvenile fish and these animals are therefore less able to avoid impacts. Juvenile fish are likely to occur throughout the Proposed Development fish and shellfish ecology study area, with some species using offshore areas as nursery habitats while inshore areas are more important as nurseries for other species (see section 9.7 and volume 3 appendix 9.1). Due to the temporary increases in SSC associated with winter storm events and the occurrence of juveniles in inshore areas (where SSCs are typically higher), it can be expected that most fish juveniles expected to occur in the Proposed Development fish and shellfish ecology study area (see Table 9.11   Open ▸ for species with nursery grounds overlapping the Proposed Development fish and shellfish ecology study area) will be largely unaffected by the low level temporary increases in SSC, as the concentrations are likely to be within the range of natural variability (generally <5 mg/l but can increase to over 100 mg/l during storm events/increased wave heights) for these species and will reduce to background concentrations within a very short period (approximately two tidal cycles).
121. A study by Appleby and Scarratt (1989) found development of eggs and larvae have the potential to be affected by suspended sediments at concentrations of thousands of mg/l. Modelling undertaken of SSC associated with the Proposed Development fish and shellfish ecology study area construction phase identified peak maximum concentrations of 2,500 mg/l predicted in the dumping phase of sand wave clearance activities at the release site. These concentrations of SSC may affect the development of eggs and larvae, however, these concentrations are only expected to be present in the immediate vicinity of the release site with dispersion of the released material continuing on successive tides. Average increases in SSC associated with sand wave clearance activities are predicted to be of the order of less than 100 mg/l. These levels are unlikely to affect the development of eggs and larvae.
122. Many shellfish species, such as edible crab, have a high tolerance to SSC and are reported to be insensitive to increases in turbidity; however, they are likely to avoid areas of increased SSC as they rely on visual acuity during predation (Neal and Wilson, 2008). Berried crustaceans (e.g. European lobster and Nephrops) are likely to be more vulnerable to increased SSC as the eggs carried by these species require regular aeration. Increased SSC within the Proposed Development fish and shellfish ecology study area (potential habitat for egg bearing and spawning Nephrops, particularly along the Proposed Development export cable corridor) will only affect a small area at any one time and will be temporary in nature, with sediments settling to the seabed quickly following disturbance (see assessment of magnitude above). Nephrops are not considered to be sensitive to increases in SSC or subsequent sediment deposition, since this is a burrowing species with the ability to excavate any sediment deposited within their burrows (Sabatini and Hill, 2008).
123. The species likely to be affected by sediment deposition are those which either feed or spawn on or near the seabed. Demersal spawners within the Proposed Development fish and shellfish ecology study area include sandeel. Spawning areas for sandeel occur within the Proposed Development fish and shellfish ecology study area, however sandeel eggs are likely to be tolerant to some level of sediment deposition due to the nature of re-suspension and deposition within their natural high energy environment. Therefore, effects on sandeel spawning populations are predicted to be limited. Sandeel populations are also sensitive to sediment type within their habitat, preferring coarse to medium sands and showing reduced selection or avoidance of gravel and fine sediments (Holland et al., 2005). This is as identified by the FeAST tool as the pressure ‘siltation changes’ (low) which has identified that sandeel have medium sensitivity to this impact (Wright et al., 2000). Therefore, any increase in the fine sediment fraction of their habitat may cause avoidance behaviour until such time that currents remove fine sediments from the seabed, although modelled sediment deposition levels are expected to be highly localised and at very low levels (less than 10 mm).
124. With respect to the effects of sediment deposition on herring spawning activity, it has been shown that herring eggs may be tolerant of very high levels of SSC (Mesieh et al., 1981; Kiorbe et al., 1981). Detrimental effects may be seen if smothering occurs and the deposited sediment is not removed by the currents (Birklund and Wijsmam, 2005), however this would be expected to occur quickly (i.e. within a couple of tidal cycles) with such a small amount of sediment deposition being forecast. Furthermore, the relatively limited amount of suitable sediments for herring spawning and the mapping of the core herring spawning habitats well outside the Proposed Development fish and shellfish ecology study area would also limit the potential for effects on herring spawning.
125. Based on the increase in sensitivity of herring eggs to the smothering effects of increased sediment deposition, herring is deemed to be of medium vulnerability, high recoverability and of regional importance, and therefore the sensitivity of this receptor is considered to be medium.
126. All other fish and shellfish ecology IEFs in the Proposed Development fish and shellfish ecology study area are deemed to be of low to medium vulnerability, high recoverability and local to national importance. The sensitivity of these IEFs is therefore considered to be low.

Diadromous Species

127. Diadromous fish species known to occur in the area are also expected to have some tolerance to naturally high SSC, given their migration routes typically pass through estuarine habitats which have background SSC which are considerably higher than those expected in the offshore areas of the Proposed Development northern North Sea fish and shellfish ecology study area. As it is predicted that construction activities associated with the Proposed Development will produce temporary and short lived increases in SSC, with levels well below those experienced in estuarine environments, it would be expected that any diadromous species should only be temporarily affected (if they are affected at all). Any adverse effects on these species are likely to be short term behavioural effects (i.e. avoidance) and are not expected to create a barrier to migration to rivers or estuaries used by these species in the Proposed Development northern North Sea fish and shellfish ecology study area.
128. Diadromous fish species IEFs in the Proposed Development fish and shellfish ecology study area are deemed to be of low vulnerability, high recoverability and national to international importance. The sensitivity of the receptors is therefore, considered to be low.

Significance of the Effect

Marine Species

129. Overall, the magnitude of the impact is deemed to be low and the sensitivity for most fish and shellfish IEFs is considered to be low to medium. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
130. For herring, the magnitude of the impact is deemed to be low and the sensitivity is considered medium. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
131. For Nephrops and lobster, the magnitude of the impact is deemed to be low and the sensitivity is considered low. The effect will, therefore, be of negligible to minor adverse significance, which is not significant in EIA terms.

Diadromous Species

132. Overall, the magnitude of the impact is deemed to be low and the sensitivity of the receptors is considered to be low. The effect will, therefore, be of negligible to minor adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

133. No additional fish and shellfish ecology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.

Operation and Maintenance Phase

Magnitude of Impact

134. Operation and maintenance activities within the Proposed Development fish and shellfish ecology study area will lead to an increase in SSCs and associated sediment deposition, including repair and reburial of inter-array, OSP/Offshore convertor substation platform interconnector and offshore export cables using similar methods as those for cable installation activities (e.g. jet trenching), undertaken at intervals during the 35-year operation and maintenance phase (see Table 9.15   Open ▸ ).
135. Any suspended sediments and associated deposition will be of the same magnitude as, or lower than, the construction phase. Volume 2, chapter 7 predicts the magnitude of SSC to be negligible and therefore, for the purposes of this assessment, the impacts of the operation and maintenance activities (i.e. cable repair and reburial) are predicted to be no greater than those for construction.
136. The impact is predicted to be of local spatial extent, short term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptors directly. The magnitude is therefore considered to be low.

Sensitivity of the Receptor

137. The sensitivity of the fish and shellfish IEFs, for both marine and diadromous species, can be found in the construction phase assessment (see paragraph 120).

Significance of the Effect

Marine Species

138. Overall, the magnitude of the impact is deemed to be low and the sensitivity for most fish and shellfish IEFs is considered to be low to medium. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
139. For herring, the magnitude of the impact is deemed to be low and the sensitivity is considered medium. The effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.
140. For Nephrops and lobster, the magnitude of the impact is deemed to be low and the sensitivity is considered low. The effect will, therefore, be of negligible to minor adverse significance, which is not significant in EIA terms.

Diadromous Species

141. Overall, the magnitude of the impact is deemed to be low and the sensitivity of the receptor is considered to be low. The effect will, therefore, be of negligible to minor adverse significance, which is not significant in EIA terms.

Secondary Mitigation and Residual Effect

142. No additional fish and shellfish ecology mitigation is considered necessary because the likely effect in the absence of further mitigation (beyond the designed in measures outlined in section 9.10) is not significant in EIA terms.

Decommissioning Phase

Magnitude of Impact

143. Decommissioning of the infrastructure within the Proposed Development fish and shellfish ecology study area will lead to increases in SSCs and associated sediment deposition. The maximum design scenario is represented by the cutting and removal of piled substructures at an agreed depth below the level of the seabed for partial removal, removal of suction caisson foundations, removal of inter-array, OSP/Offshore convertor substation platform interconnector and offshore export cables using jet trenching which mobilises material from a depth of up to 3 m deep in a trench of up to 2 m wide.
144. Decommissioning of foundations is predicted to result in increases in suspended sediments and associated deposition that are no greater than those produced during construction, and likely to be smaller as seabed clearance is less likely to be required. For the purpose of this assessment, as described in volume 2, chapter 7, the impacts of decommissioning activities are predicted to be no greater than those for construction (see paragraph 113 et seq.).
145. The impact is predicted to be of local spatial extent, short term duration, intermittent and high reversibility. It is predicted that the impact will affect the receptor directly. The magnitude is therefore considered to be low.